A medium sized species with a laterally compressed rear portion of the body. Maximum length 900 mm and maximum size 6.8 kg; usually <500 mm and <2 kg. The head is large and four pairs of barbels surround the large mouth, with its thick fleshy lips. The first dorsal fin is short but high, just behind the head, and has a stout, serrated spine at the front of the fin. The second dorsal fin is continuous with the caudal and anal fins, hence the species’ alternative common name of Eel-tailed catfish. The skin is smooth, with no scales.
The back of adults is usually olive-green to brown, and the belly whitish. Juveniles tend to be grey-brown, mottled with darker blotches.
Freshwater catfish is a benthic species that prefer slow-flowing streams and lake habitats. A radio-tracking study in Tahbilk Lagoon in northern Victoria revealed that freshwater catfish make extensive use of cover such as wood and macrophytes. Fish were nearly always located near the margins of the lagoon in shallow depths, especially during the day, whereas at night they tended to be located slightly further from the shore.
Individuals are sexually mature at 3–5 years of age and spawn in spring and summer when water temperatures are 20–24°C. The nest is a circular to oval depression, 0.6–2.0 m in diameter, and in 0.2–1.35 m water depth, constructed from pebbles and gravel, with coarser material in the centre. The nest is constructed by the male.
Courtship is elaborate with the male attracting the female to the nest, then both sexes weaving and circling, and the male nudging the females flank, with the female then arching around the male’s head and violently agitating her pectoral fins. This behavioural sequence is repeated several times over 15–20 minutes before the female leaves.
The eggs are large (2.6–4 mm diam., mean 3.4 mm), non-adhesive, settle into the interstices of the coarse substrate, and take up to seven days to hatch. The male fish remains with the nest to fan, clean and guard the eggs. In an artificial lake, multiple spawning in a single nest (both sequentially and concurrently) in a season have been observed. Larvae are about 5–8 mm standard length at hatching, growing to ~12 mm at 10–14 days old. Larvae can actively disperse by 16 days of age and leave the nest. Juveniles in the Macquarie River were approximately 42-, 80- and 120-mm length at 50, 100 and 150 days respectively.
Freshwater catfish are considered generally sedentary in rivers; adults in the lower Murray River show very limited movement (<10 km) compared to Murray cod and golden perch. In Tahbilk Lagoon most fish typically had limited ranges (<600 m), although they occasionally moved more extensively (up to 1.5 km) between floodplain and riverine habitats. Fish moved over much greater areas at night compared to during the day. Tagged fish generally became more active around 1-2 hrs before sunset, frequently shifted locations within the lagoon through the night, and then returned home shortly after sunrise.
A recent study in the semi-arid Moonie River in Qld, found although most catfish (58%) were sedentary and didn’t leave their home waterhole during river rises, 42% of tagged catfish did move out of their home waterholes. Of the fish that moved, approximately 55% of fish moved upstream, with an average distance of 25 km, and 45% moved downstream, on average 13 km, but movements of 60-70 km were recorded in both directions. Of the fish that moved, most returned to their home waterhole as the flow event subsided or during subsequent flow events. Most movement occurred between November and May when water temperatures were between 15-28 °C, with fish moving on large to very large flows.
Similarly in a tributary of the Pioneer River in coastal, central Queensland, the species was largely sedentary with 29% not moving, 64% moving between pools, and 7% moving between river reaches. The maximum distance moved was 17 km downstream. Movement between pools was mostly at dawn and dusk, presumably to feed.
In the Mehi and Gwydir rivers in the Northern MDB, freshwater catfish were less likely to move on an environmental flow release following higher preceding flows. In this study, males had a higher likelihood of movement than females during the breeding season but were less likely to move with increasing temperatures.
Freshwater catfish is predominantly an opportunistic carnivore and the adult diet consists mainly of shrimps, freshwater prawns and yabbies, with aquatic insects, snails and small fishes also important. Aquatic insects are more important in the diet of juvenile fish.
A Freshwater catfish nest. Photographer: Gunther Schmida.
This catfish was widespread throughout the Murray-Darling Basin, but generally in the lower, slow-flowing rivers. It (and a number of suspected cryptic species) is also found in coastal rivers from southern NSW to northern Qld. Most riverine populations have declined significantly since the late 1970s/early 1980s, and the species is extinct or no longer common in many areas where it was formerly abundant and is listed as threatened in NSW and Vic. Some populations in impoundments seem to be faring better. The species was relatively abundant in the Qld portion of the Basin until recently. It is still common in the upper Condamine River but has effectively disappeared from the Paroo and is now in relatively low numbers in the lower Condamine and Warrego rivers.
In monitoring for the Sustainable Rivers Audit (2004–13), a total of only 380 individuals (0.17% of the total fish catch) were caught with 89% of these coming from upland (233 individuals), slopes (71) or montane (36) sites and only 40 from lowland sites. 39% of SRA records were from the Border rivers and 38% from the Gwydir valley, with no other valley contributing >8% of the total. The MDB Fish Survey (2014/15–2021/22) only recorded a total of 260 individuals with only 33 from lowland zones (<200m elevation), mostly in the Lower Murray. It has been stocked into some farm dams and lakes where it can establish breeding populations.
Numerous threats have contributed to the decline in this species. Concern has been expressed about the potential impacts of Carp (egg predation or nest disturbance) and Redfin perch on riverine populations. Cold-water pollution below dams, barriers to movement, sedimentation of nests, and changes to natural flow regimes are also suspected as causes of declining local populations, with breeding in tributaries assuming significant importance for the species. The lack of formal recognition as a threatened species nationally and in most states has hampered conservation efforts.
Burndred et al. 2017, 2018; Carpenter‐Bundhoo et al. 2022; Clunie & Koehn 2001a,b; Davis 1977a,b,c; Kerezsy 2022b; Koehn et al. 2020a; Koster et al. 2015; Lake 1967; Marshall et al. 2016; Merrick & Schmida 1984; NSW FSC 2008b; Pollard et al. 1996; Pusey et al. 2004; Reynolds 1983; Rourke & Gilligan 2015; Stocks et al. 2019.
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